U.S. Pat. No. 4,375,021, in the name of Franco P. Pardini and Francesco DeVizzi, describes the use of a magnetic assembly arranged about a pair of circuit breaker contacts for electrodynamically repulsing the contacts and for electrodynamic motivation of the arcs that occur when the contacts become separated. The arc chute used within the breaker for cooling and extinguishing the arc is formed by enfolding a metal strip partially around an insulating support substrate.
U.S. Pat. Nos. 2,005,684 and 2,551,822 both teach arc chute assemblies that contain a composite structure of one material having good arc resistant properties such as asbestos alongside another material having good physical support properties.
When the Pardini et al. circuit breaker is used to interrupt short circuit current at rated voltages in excess of 400 volts, it has been determined that the arc chute side supports interfere with the arc extinguishing process at higher arc temperatures and higher arc voltages. Asbestos materials, having excellent high temperature and electrical resistance properties, are no longer available to the electrical industry by legislative mandate.
U.S. Pat. No. 4,733,032 entitled "Electric Circuit Breaker Arc Chute Composition" describes a two-layer laminate structure for arc plate side supports wherein the layer facing the arc consists of a melamine resin impregnated cloth fiber while the opposite layer consists of a melamine resin impregnated glass fiber. The opposite layers must be color-coded to insure that the cloth fibers face the arc rather than the glass fibers. Should the glass fibers become subjected to the temperatures generated within the arc chute, the low ionization potential elements within the glass fibers would become ionized and thereby interfere with the arc extinction process.
U.S. Pat. No. 4,748,301 entitled "Electric Circuit Breaker Arc Chute Composition" describes a three-layer laminate structure for arc plate side supports. This Patent uses materials similar to those described within the aforementioned U.S. Pat. No. 4,733,032 and includes an extra layer to the laminate structure to eliminate the need for orienting the arc plates with respect to the arc.
U.S. Pat. No. 4,511,773 entitled "Molding Composition for Arc Circuit Breakers", which Patent is incorporated herein for reference purposes describes a ceramic arc chute assembly consisting essentially of a mixture of wollastonite powder calcined with phosphoric acid. The composition is an effective substitute for asbestos arc chute assemblies but is quite expensive to manufacture and requires vigorous process control.
U.S. Pat. No. 3,407,155 describes the use of wollastonite fibers as fillers for circuit breaker housings to improve the arc resistant properties of such housings. U.S. Pat. No. 2,917,607 entitled "Arc Resistant Molded Members" teaches the elimination of arc chutes within circuit breakers wherein the circuit breaker housings are fabricated from thermoset resins such as melamine containing inorganic fillers such as wollastonite.
The instant invention proposes the use of specific wollastonite fibers suspended within melamine resin as a substitute material for the calcined wollastonite arc chute assembly described within the aforementioned U.S. Pat. No. 4,511,773.